The Indian Space Research Organisation (ISRO) has successfully completed the docking of its SpaDeX satellites, achieving a key milestone in space technology. This comes days after the satellites were brought within 3 meters of each other. An official announcement is expected soon, pending video confirmation. The docking follows two earlier delays on January 7 and 9 due to technical issues, with the satellites originally launched on December 30.

On January 12, ISRO announced the successful completion of a trial to bring two satellites within 15 meters and subsequently 3 meters of each other. In a statement, ISRO noted, “A trial attempt to reach up to 15 m and further to 3 m is done. Moving back spacecrafts to safe distance. The docking process will be done after analysing data further.” This marked a critical step leading up to the successful docking of the SpaDeX satellites.

ISRO initially planned to make the docking of the two satellites a public event. However, after two consecutive postponements, a senior official stated that the docking process “is on track,” but the agency has decided to proceed with the docking first and inform the public afterward.

The postponement of the SpaDeX docking schedules coincided with a leadership transition at ISRO. On January 7, the Central government announced the appointment of V. Narayanan as ISRO's new director, and he officially assumed charge on January 14.

The SpaDeX (Space Docking Exercise) mission serves as a technology demonstrator, showcasing the capability to dock two small satellites. These satellites were launched aboard the PSLV on December 30.

The SpaDeX mission demonstrates a critical technology for future Indian space endeavors, including Chandrayaan-4, which aims to return lunar samples to Earth. In this mission, a transfer module carrying Moon samples will dock with a re-entry module designed to endure Earth's atmospheric re-entry.

Docking technology will also be essential for constructing the Bharatiya Antariksh Station, with its first module scheduled for launch in 2028. The station will comprise five modules, launched separately and assembled in space. Additionally, the human mission to the Moon, planned for no earlier than 2040, will also require advanced docking capabilities.

For the SpaDeX mission, ISRO launched two spacecraft—SDX01 (Chaser) and SDX02 (Target)—on December 30 into a low-Earth circular orbit. They were initially set 20 km apart to enable a gradual rendezvous, culminating in a successful docking.

In the SpaDeX mission, after starting with an initial inter-satellite separation of 20 km, the Chaser satellite gradually approached the Target satellite in a series of precise maneuvers. The distance was reduced in stages to 5 km, 1.5 km, 500 m, 225 m, 15 m, and finally 3 m before achieving the final docking of the two spacecraft.

ISRO had initially scheduled the docking of the SpaDeX satellites for the morning of January 7, following their successful launch and release into orbit. However, on January 6, the agency announced a postponement, shifting the docking to January 9. The delay was due to the need for further validation through ground simulations based on an identified abort scenario.

On January 8, ISRO reported that it had initiated the drift on the spacecraft to reduce the distance from 500 m to 225 m in preparation for docking. However, the agency also announced that the docking would be postponed once again to January 9 due to a technical issue.

On January 9, ISRO announced that the drift between the two spacecraft had been arrested and they were put on a slow drift course to bring them closer to each other. The agency stated that they expected to reach the initial conditions for docking by the following day.

A former ISRO official highlighted that the docking experiment was crucial for multiple future missions, including Chandrayaan-4 and the planned Indian space station. The Chandrayaan-4 mission will involve several docking and undocking maneuvers, both in Earth’s orbit and lunar orbit.

According to P. Veeramuthuvel, the ISRO scientist and project director for the successful Chandrayaan-3 mission, two modules will be launched by separate vehicles into GTO, then travel together to the Moon. One module will remain in lunar orbit while the other will land on the Moon's surface to collect samples. The module that lands on the Moon will then return to lunar orbit and dock with the module that had remained in orbit. This sequence of maneuvers is a vital part of the Chandrayaan-4 mission's objectives.

P. Veeramuthuvel further explained that in the Chandrayaan-4 mission, the samples collected from the Moon will be transferred from the ascent module to the transfer module. Once this transfer is complete, the ascent module will be undocked, and the transfer module will exit the Moon’s sphere of influence. It will then travel towards Earth, performing a trans-Earth injection to re-enter Earth's orbit. Finally, the transfer module will release the re-entry module, which will then descend through Earth's atmosphere and land at a designated target site.